ATP diphosphohydrolase is responsible for ecto-ATPase and ecto-ADPase activities in bovine aorta endothelial and smooth muscle cells.

An ATP diphosphohydrolase (EC 3.6.1.5) is an enzyme hydrolyzing pyrophosphate bonds in nucleoside di- and triphosphates with broad substrate specificity in the presence of divalent cations. The ATPase and ADPase activities in the enzyme purified to homogeneity from bovine aortic vessel wall were insensitive to oligomycin, ouabain, and various protease treatments, and sensitive to azide and Ap5A. Bovine aorta endothelial and smooth muscle cells were cultured separately to characterize the ectonucleotidase activities. The activities were dependent on the addition of divalent cations and had broad substrate specificity. The ecto-ATPase and -ADPase activities were insensitive to oligomycin, ouabain, and protease treatments, and sensitive to azide and Ap5A. No enzyme degrading only ADP was found in the aortic vessel wall. Moreover, antiserum raised against purified ATP diphosphohydrolase inhibited the ecto-ATPase and -ADPase activities. These results indicated that ecto-ATPase and ecto-ADPase are not separate enzymes but are expressed by one enzyme, ATP diphosphohydrolase.